This invention relates to a bipolar transistor circuit that is substantially used for generating a two-terminal negative resistance that is useful in compensating for losses and improving the quality (Q) factor of integrated resonators. More specifically, the invention provides a means for generating a broadband negative resistance that is electronically adjustable over a wide range of resistive losses.
High-frequency resonators are critical components in oscillators, RF circuits and other circuits. Such resonators are very susceptible to degradation by losses and it is often necessary to separate the resonator from the active semiconductor circuit. The resulting hybrid circuit is generally larger, more difficult to manufacture, and more expensive than a fully integrated circuit. Current circuits use mixed field effect transistor (FET) bipolar processes, or PIN diodes, for adjustment, and rely on reactive components such as inductors or variable capacitors in order to function.
Presently negative resistance circuits are used to enhance Q resonators. The majority of the Q resonators are based on field effect transistors rather than bipolar transistors. This greatly limits their use in the fastest large-scale-integrated circuits such as those using InP and SiGe heterojunction bipolar transistors. Only a small selection of Q resonators allow for the negative resistance to be electronically adjusted, and these either have a small range of adjustment or employ variable reactances in feedback that substantially limit the bandwidth and applicability of the circuit.
Bandpass delta-sigma modulators for signal processing require high-Q resonators with a high signal-to-noise ratio to effectively convert data. However, even the best passive resonators often suffer from prohibitively large losses when integrated onto semiconductor substrates, and implementing the resonator off-chip leads to parasitics and signal delays that cause instability in high performance modulators.
Therefore it would be desirable to integrate circuit components onto a single semiconductor chip in order to reduce the physical size and power consumption of circuit components. This integration could be achieved by inventing an electronic means for improving the Q factor of on-chip resonators. Such an electronic means would enable the creation of high-performance bipolar RF circuits with a minimum of external components. The invention would need to be an electronically adjustable negative resistance circuit configured such that the level of loss compensation would be continuously variable over a wide range of losses. Such a system would ultimately improve performance, reduce cost, increase system versatility, and reduce size.
The present invention provides an integrated circuit that utilizes an electronic means for improving the Q factor of on-chip resonators. The invention allows for the creation of high-performance bipolar RF circuits with a minimum of external components. The invention utilizes an electronically adjustable negative resistance circuit that is configured to provide a level of loss compensation that is continuously variable over a wide range of losses. The invention results in a circuit having improved performance characteristics, increases the system""s versatility, while reducing its size, and further, the costs associated with fabrication and design are generally reduced.
One embodiment of the present invention provides a solution for improving the Q factor, and compensating for loses, in integrated resonators. The embodiments described herein describe a bipolar transistor circuit that has a variable transconductance cell connected with positive feedback to generate a negative resistance at its output terminals.
Another embodiment of the invention relates to a method for generating a two-terminal negative resistance, in a bipolar transistor circuit, using components commonly available in bipolar transistor processes. While yet another embodiment of the invention relates to a circuit element that produces an adjustable negative resistance ranging from a minimum to essentially negative infinity, where the negative resistance is electronically adjustable and continuously variable. Another embodiment of the invention relates to a circuit element that exhibits an increase in current as the applied voltage is decreased, wherein the applied voltage varies due to resistance caused by such factors as imperfectly conducting materials or poorly insulating substrates.